Tissue stabilizing implant

ABSTRACT

The present invention relates to an implant for stabilizing body tissue. The implant includes a core formed of a material which expands when contacted with liquid and a retainer which at least partially encloses the core.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.10/279,451, filed Oct. 24, 2002. The aforementioned application Ser. No.10/279,451 is itself a continuation of application Ser. No. 09/798,870,filed Mar. 1, 2001, now U.S. Pat. No. 6,503,277 B2. The aforementionedapplication Ser. No. 09/798,870 is itself a continuation of applicationSer. No. 09/602,743, filed Jun. 23, 2000, now U.S. Pat. No. 6,361,565.The aforementioned application Ser. No. 09/602,743 is a continuation ofapplication Ser. No. 09/263,006, filed Mar. 5, 1999, now U.S. Pat. No.6,132,472. The aforementioned application Ser. No. 09/263,006 is itselfa continuation of application Ser. No. 08/834,028, filed Apr. 11, 1997,now U.S. Pat. No. 5,888,219. The aforementioned application Ser. No.08/834,028 is itself a divisional of application Ser. No. 08/590,193,filed Jan. 23, 1996, now U.S. Pat. No. 5,662,710. The aforementionedapplication Ser. No. 08/590,193 is itself a divisional of applicationSer. No. 08/273,028, filed Jul. 8, 1994, now U.S. Pat. No. 5,545,222.The aforementioned application Ser. No. 08/273,028 is itself adivisional of application Ser. No. 07/728,247, filed Aug. 12, 1991, nowU.S. Pat. No. 5,329,846. The benefit of the earlier filing dates of theaforementioned applications and patents is claimed.

BACKGROUND OF THE INVENTION

[0002] Tissue grafting, including bone grafting, is well known. Tissuesuch as bone is removed from one part of a body (the donor site) andinserted into tissue in another (the host site) part of the same (oranother) body. It is desirable to be able to remove a piece of tissuegraft material which is the exact size and shape needed for the hostsite where it will be implanted. However, it is rarely possible to dothis.

[0003] Accordingly, various tissue grafting techniques have been triedto solve this problem. For example, U.S. Pat. No. 4,678,470, granted toNashef, discloses a method of creating bone graft material by machininga block of bone to a particular shape, or by pulverizing and milling it.The graft material is then tanned with glutaraldehyde to sterilize it.This process can produce bone plugs of a desired shape.

[0004] In the Nashef process, the exogenic bone material selected forthe graft is presumably dead at the beginning of the process. Theprocess of pulverizing or milling the bone material destroys thestructure of the bone tissue. The step of tanning it with glutaraldehydethen renders the graft material completely sterile. This condition isnot conducive to graft healing and ingrowth. Specifically, applicant hasfound that it is desirable to maintain graft tissue in a living stateduring the grafting process. The use of living tissue in a graft willpromote bone healing.

SUMMARY OF THE INVENTION

[0005] The present invention is a tissue press for shaping orcompressing a piece of tissue. The press includes first and secondmembers movable relative to each other. First and second formingelements of different predetermined shapes are positionable on the firstand second members on opposite sides of the piece of tissue. The firstand second members are moved toward each other to shape or compress thetissue between the first and second forming elements.

[0006] Means are preferably provided for monitoring and controlling theamount of force or pressure applied to the piece of tissue, in order tomaintain the tissue in a viable living condition. Means may also beprovided for draining off fluid from compressed tissue, so that thetissue can be implanted in a compressed state and imbibe fluid from thehost site.

[0007] The present invention is also a method of reshaping tissue foruse as graft material comprising the steps of determining the shapewhich the tissue should possess as graft material; providing a tissuepress, selecting forming elements adapted to press tissue approximatelyto the desired shape, and placing the forming elements on the tissuepress; placing the tissue in the tissue press between the formingelements; operating the tissue press to shape the tissue between theforming elements to give the tissue the desired shape; and controllingthe pressure on the tissue during the shaping step to minimize damage toor necrosis of the tissue.

[0008] The present invention is also a method which includes the stepsof determining the shape and size which the tissue should possess asgraft material; placing the tissue in a tissue press having formingelements adapted to press tissue approximately to the shape and sizedesired; compressing the tissue in the tissue press to give the tissuethe shape and size desired; controlling the pressure on the tissueduring the compressing step to minimize damage to or necrosis of thetissue; and draining off fluid expressed during the compressing step.

[0009] In accordance with another feature of the present invention, aretainer is provided for retaining tissue graft material in itscompressed state. The retainer is placed around the compressed graft.The retainer can help to maintain the graft in a compressedconfiguration or in a specific shape for a period of time long enough tobe placed in the body. The retainer may be made of a material whichexpands after it is placed in the body, to mechanically interlock thegraft to the body.

GENERAL DESCRIPTION OF THE INVENTION

[0010] With the apparatus and method of the present invention, bone orother tissue can be compressed or reshaped or both, while preserving thetissue alive.

[0011] Often, reshaping of graft tissue is necessary to obtain the bestpossible graft. For example, in an anterior cruciate ligamentreconstruction, the graft material which is removed usually has atriangular cross-sectional configuration. This graft material is placedin an opening in bone formed by drilling with a round drill. When thetriangular graft material is placed in the round opening, there isminimal physical contact between the graft material and the surroundingbone. This reduces the holding power of the graft and also reduces theingrowth ability of the graft.

[0012] Thus, an important feature of the present invention is that boneor other tissue such as ligament is reshaped while still leaving it in awhole condition and without substantial tissue damage. The tissue isplaced in the tissue press of the present invention and sufficient forceis applied to reshape the tissue to the desired shape—for example, acylindrical shape as needed for an anterior cruciate ligamentreconstruction. Excessive pressure on the tissue, which can damage orkill the tissue, is avoided as described below. A properly shaped graftis thus provided which is still in a living condition.

[0013] Compression of graft tissue is also sometimes desirable.Generally, tissue is stronger when it is denser. Compressing grafttissue increases its density and thus strengthens the graft tissue. Thegraft tissue also stays together better.

[0014] For example, a tendon is made of a plurality of fibers. Theindividual fibers are weak when separated or unraveled. If a tendongraft is implanted with the fibers in a loose condition, the graft isweak. On the other hand, if prior to implantation the tendon graft iscompressed to orient and pack the fibers tightly, then the entire groupof fibers acts as one whole unit and the graft is much stronger.Therefore, compressing the tendon graft gives it more mechanicalintegrity—making a smaller tendon graft much stronger.

[0015] Similarly, bone tissue is stronger and better able to bear forcewhen it is denser and more compact. Compressing bone graft tissue priorto implantation produces a stronger graft. Compression of bone or othertissue also allows a surgeon to convert a larger irregular shape into asmaller specific shape. Thus, the surgeon when removing the graftmaterial from the donor Site is not limited by the conditions at thehost site but can remove the graft material in the best way possiblefrom the donor site. Similarly, the surgeon when implanting the graftmaterial at the host site is not limited by the shape of the materialremoved (as dictated by the conditions at the donor site) but canimplant the graft material in the best way possible to fit theconditions at the host site.

[0016] The anterior cruciate ligament, for example, attaches to thefemur and tibia at specific isometric locations. When the ligament isbeing replaced in an anterior cruciate ligament reconstruction, typicaluncompressed graft material can be many times the size of thoselocations. In such a case it is necessary to drill openings much largerthan desired in the bone to attach the new ligament. The graft tendonthen tends to fall eccentrically in this larger opening, the functionalanatomy of the ligament can not be recreated, and the functioning of theknee joint is compromised.

[0017] However, if the graft material for the new ligament is compressedin accordance with the present invention, its size can be reducedsubstantially. This allows the surgeon to drill a substantially smalleropening in the bone to attach the new ligament/graft structure, so as torecreate the functional anatomy of the ligament.

[0018] With the present invention, it is also possible to make acomposite graft. For example, the graft material for an anteriorcruciate ligament reconstruction is preferably tendon in the middle withbone at both ends. In accordance with the apparatus and method of thepresent invention, bone tissue can be compressed around the ends oftendon tissue to form a substitute anterior cruciate ligament moreclosely approximating the original.

[0019] It should also be noted that tissues other than bone and tendoncan be worked with the tissue press. For example, a surgeon can harvestliver cells or pancreas cells and then compress them into a particularshape. They can then optionally be placed into a sack or some type ofstructural support which can be introduced into the body.

[0020] With the present invention, graft material can be formed intoalmost any shape. A specific pair of forming (mold) parts, having adesired predetermined shape, are positioned on the tissue press, and thetissue is shaped or compressed between the forming elements. In additionto three-dimensional shaped parts, it is also possible to make a flatpiece of graft material. For example, shaved skin can be placed on aflat plate, perhaps on a retaining mesh. The cells are then subjected topressure to adhere them together. A flat, even, piece of graft materialis formed which is suitable for skin grafting.

[0021] Compressing graft material in accordance with the presentinvention also allows the surgeon to build up a larger piece of graftmaterial out of several smaller parts. Sometimes a relatively largepiece of graft material is needed for a particular host site. It isoften not feasible to take such a large piece of graft material withoutdamaging the donor area. To avoid this problem, several smaller piecesof graft material are placed in the tissue press and pressure is used toat least temporarily form the smaller parts together as one largerwhole. The larger graft piece is then inserted into the host site.

[0022] Compressing graft material in accordance with the presentinvention also aids in introducing additional materials to the graftmaterial. These additional materials could be antibiotics, bone growthenhancers, tri-calcium phosphate, fibrin, allograft or autograftmaterial, etc. When added to the graft material under pressure, theadded materials adhere to and become a part of the graft material andnot merely something added to the surface of it. By combiningphysiologic solutions or a carrier such as a gelatin, polysaccharides,antibiotics or synthetic bone materials to the compressed bone, forexample, it is possible to create a plug of living bone with the othermaterials added into it. This plug has the graft properties of the bonetissue in the plug, as well as the properties of the added material.

[0023] When tissue is compressed, fluid may be forced out of (expressedfrom) the tissue. If tissue in this compressed and defluidized state islaid back in a tissue pouch or in a bone hole, body fluids from the hostsite are absorbed by the graft material. This imbibition causes swellingof the graft material and thus creates a mechanical interlock betweenthe graft and the host. Such a mechanical interlock is not produced witha typical implantation process in which graft tissue is not compressed.Further, the swelling (enlarging) of the graft material allows the graftmaterial to fill an opening of any given shape with a perfect fit of thegraft material therein.

[0024] As noted above, applicant has found that it is desirable tomaintain bone graft tissue in a living state during the graftingprocess. It is important not to kill tissue used in grafting because theliving graft cells provide a superior substrate for grafting and graftviability and improved tissue healing. There is significantly fasterincorporation of living tissue than of dead tissue. The cells and thetissue that are implanted into the body therefore need to be maintainedin a viable condition.

[0025] Excess pressure on tissue can cause destruction of the tissue,disorganization of the tissue fibers and irregular mechanical structurewhich can damage the tissue graft. Thus, a feature of the presentinvention is that the pressure or force on the tissue being reshaped orcompressed is monitored and controlled. Pressure can be monitored bysuitable pressure sensors and readouts such as a pressure gauge.Pressure can be controlled by force limiting means such as a torquewrench or similar device.

[0026] The desired pressure levels may vary. For example, it may bedesirable to provide a higher compressive force for cortical bone thanfor cancellous bone. Similarly, it may be desirable to provide a highercompressive force for bone than for tendon tissue. The appropriate levelof pressure or force is selectively available with the tissue press.

[0027] A separate device or structure can be used to maintain grafttissue in the compressed state prior to and during implantation. Thisseparate device or structure can be a mesh sack, a ring around acylindrically shaped graft material, etc. This additional retainerstructure can assist the surgeon in introducing the graft tissue intothe body in the compacted condition, to provide a denser stronger graftand to allow imbibition for creating a mechanical interlock. Theretainer can be made of a material which expands when placed in thebody, to provide a mechanical interlock for the graft tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The foregoing and other features of the present invention willbecome apparent to one skilled in the art upon a consideration of thefollowing description of the invention with reference to theaccompanying drawings, wherein:

[0029]FIG. 1 is a top plan view of a tissue press embodying the presentinvention;

[0030]FIG. 2 is a top plan view of a tissue press similar to the tissuepress of FIG. 1 and having a pressure sensing and monitoring mechanism;

[0031]FIG. 3 is an elevational view of the tissue press of FIG. 2;

[0032]FIGS. 3A and 3B illustrate a tissue press having means forremoving excess tissue after compression;

[0033]FIGS. 4A-4F illustrate a plurality of different forming elementsfor use in the tissue press of FIGS. 1-3;

[0034]FIG. 5 is a view of a tissue press in accordance with a secondembodiment of the invention;

[0035]FIG. 6 is a view of a tissue press in accordance with a thirdembodiment of the invention;

[0036]FIG. 6A illustrates a tissue press having means for limiting theamount of pressure applied to the tissue;

[0037]FIGS. 7 and 7A illustrate a composite tissue graft such ascompression of bone around tendon;

[0038]FIG. 8 is a view of a tissue press in accordance with a fourthembodiment of the invention illustrating extrusion of tissue graftmaterial;

[0039]FIGS. 9A-9F illustrate a plurality of different retainers forcompressed tissue;

[0040]FIGS. 10A and 10B illustrate an expanding tissue retainer;

[0041]FIGS. 11, 11A and 11B illustrate an expanding surgical implant;and

[0042]FIGS. 12 and 12A illustrate expanding surgical stabilizationdevices.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0043] The present invention relates to a tissue press and particularlyto a tissue press for shaping or compressing bone or other tissue. Thepresent invention is applicable to various constructions of tissueshaping or compressing apparatus. As representative of the presentinvention, FIG. 1 illustrates a tissue press 10.

[0044] The tissue press 10 includes a base 12. The base 12 has a supportsurface 14 for supporting the base 10 and thus the press 10 on a tableor other support (not shown). The base 12 has the same longitudinalcross-section throughout its width as is seen in elevation in FIG. 1.Two cylindrical pins 16 protect upwardly from the base 12. A U-shapedsaddle 18 is secured to the base 12 by screws 20. A pin opening 22extends transversely through the saddle 18.

[0045] The tissue press 10 also includes a handle 30. The handle 30 hasa connector portion 32 received between the upwardly projecting sideportions of the saddle 18 of the base 12. A pin opening 34 extendstransversely through the connector portion 32 of the handle 30. Theopening 34 is aligned with the opening 22 in the saddle 18. A pivot pin36 extends through the pin openings 34 and 22 in the handle 30 and base12, respectively, and pivotally connects the handle 30 to the base 12.

[0046] Extending from the connector portion 32 of the handle 30 is aform-supporting portion 40 of the handle 30. A channel 42 is defined onthe lower side of the form-supporting portion 40 between a pair ofchannel surfaces 44. The channel 42 extends transversely across thewidth of the form-supporting portion 40. Extending from theform-supporting portion 40 is a circular portion 46 of the handle 30.The circular portion 46 has a manually engageable surface 48 for theapplication of force to the handle 30.

[0047] A first forming element 50 is slidably received on the base 12.The first forming element 50 has two vertically extending pin openings52 which receive the pins 16 of the base 12. The first forming element50 has an upper surface 54 which includes a forming surface 56. Theforming surface 56 has a cylindrical surface portion 58. The firstforming element 50 has the same longitudinal cross-section throughoutits width as is seen in elevation in FIG. 1. It should be understoodthat the first forming element 50 can be connected with the base 12 inany other suitable manner.

[0048] A second forming element 60 is slidably received in the channel42 of the handle 30. The second forming element 60 has two projectingedges 62 which engage the channel surfaces 44 of the handle 30. Thesecond forming element 60 has a lower surface 64 which includes aforming surface 66. The forming surface 66 includes a cylindricalsurface portion 68. The second forming element 60 has the samelongitudinal cross-section throughout its width as is seen in elevationin FIG. 1. It should be understood that the second forming element 60can be connected with the handle 30 in any other suitable manner.

[0049] In operation of the press 10, a pair of forming elements 50 and60 are selected which when brought together will shape a piece of livingtissue 70 to the desired shape. For example, the forming elements 50 and60 illustrated in FIG. 1 have cylindrical surface portions which willshape tissue into a cylindrical shape suitable for insertion into around drill hole in bone. The first forming element 50 is slid onto thepins 16 on the base 12. The second forming element 60 is slid into thechannel 42 in the handle 30. A set screw 72 is tightened to secure thesecond forming element 60 to the handle 30.

[0050] The piece of tissue 70 to be shaped is placed between the firstand second forming elements 50 and 60. The tissue 70 is preferablypositioned on the forming surface 56 of the first forming element 50 asillustrated in FIG. 1. The handle 30 is then brought toward the base 12in the direction indicated by the arrow 74, by the application of forceto the handle 30. The forming surface 66 with its cylindrical surfaceportion 68 engages the tissue 70, and forces the tissue 70 against theforming surface 56 with its cylindrical surface portion 58. The tissue70 is thereby formed to the desired shape.

[0051] It should be understood that with the tissue press 10, tissue canbe reshaped only, or reshaped and compressed. The amount and type ofwork performed on the tissue depends on the particular application, andis controlled by (i) the particular forming elements selected by theoperator of the tissue press, and (ii) the amount of pressure or forceapplied to the tissue. For example, the forming elements can be selectedso that they define between them a forming chamber having the sameinitial volume as the piece of tissue to be shaped. In this case, thepiece of tissue is not compressed (that is, reduced in volume), but ismerely reshaped. Alternatively, forming elements can be selected whichwill not merely reshape the piece of tissue but also will compress it,as described above. Because the first and second forming elements 50 and60 are removably received on the base 12 and handle 30, respectively,the surgeon can easily select first and second forming elements 50 and60 to reshape or compress the tissue 70 as desired.

[0052] As discussed above, it is important to control the pressure onthe tissue in the tissue press 10. There are many ways to do this. Forexample, in the press 80 shown in FIGS. 2 and 3, a second formingelement 84 has an opening 82 which extends between its upper surface 86and its forming surface 88. An opening 90 in the handle 92 is alignedwith and in fluid communication with the opening 82. A pressure monitordevice indicated schematically at 94 is in fluid communication with theopening 90 in the handle 92, and thus with the forming surface 88 on thesecond forming element 84. The pressure monitor device 94 can be anyknown device for displaying pressure, such as a dial readout, a barmovable axially in the openings 82 and 90 in response to fluid pressure,etc. The pressure monitor device 94 displays the pressure at the formingsurface 88 of the second forming element 84. This is the pressureapplied to the tissue being pressed in the press 80. Thus, an operatorof the press 80 can observe this pressure monitor device 94 and limitthe applied force accordingly, in order to avoid tissue damage ornecrosis.

[0053] Alternatively, a strain gauge of a known construction, indicatedschematically at 96, can be placed on the forming surface 88 of thesecond forming element 84. Electric wires (not shown) transmit signalsfrom the strain gauge 96 to an electric readout device indicatedschematically at 94. The electric readout indicates electrically thepressure applied to the tissue in the press 80. Again, one can observethis pressure monitor device and limit the amount of force applied, inorder to avoid tissue damage or necrosis. It should be understood thatsimilar ways of monitoring the pressure on the tissue being pressed arethe equivalent and are thus included within the scope of the invention.

[0054] Any of the tissue presses of the present invention can includemeans for cutting off excess tissue. As an example, FIGS. 3A and 3Billustrate a tissue press 91 having an independent cutoff arm 93pivotally mounted adjacent the handle 95. The cutoff arm 93 has a bladeportion 97 operable to cut off excess tissue compressed by the tissuepress 91. The cutoff arm 93 is, of course, merely illustrative of themany equivalent structures usable to remove excess tissue after thecompressing or shaping operation. Thus, the length of the tissue graftmaterial, as well as its compressed diameter, can be selectivelycontrolled by operation of the tissue press. It should be noted thatthis cutting off process can be affected with the edges of the formingelements themselves, as illustrated in the apparatus in FIG. 5.

[0055] As noted above, the first forming element 50 and the secondforming element 60 are removably received on the base 12 and handle 30,respectively. Thus, forming elements having forming surfaces with othershapes can be easily placed in the tissue press 10, in order to shape orcompress tissue into other shapes. A few of the many shapes obtainableare illustrated in FIG. 4.

[0056]FIG. 4A, for example, illustrates the forming elements 50 and 60of FIG. 1-3 which shape tissue into a cylindrical cross-sectional shape.FIG. 4B illustrates forming elements 100 and 102 which shape tissue intoan oblong cross-sectional shape, between a forming surface 104 on thefirst forming element 100 and a forming surface 106 on the secondforming element 102. FIG. 4C illustrates forming elements 108 and 110which shape tissue into a square cross-sectional shape, between aforming surface 112 on the first forming element 108 and a formingsurface 114 on the second forming element 110.

[0057]FIG. 4D illustrates forming elements 116 and 118 which shapetissue into a triangular cross-sectional shape, between a formingsurface 120 on the first forming element 116 and a forming surface 122on the second forming element 118. FIG. 4E illustrates forming elements124 and 126 which shape tissue into a generally flat shape, between aforming surface 128 on the first forming element 124 and a formingsurface 130 on the second forming element 126. FIG. 4F illustratesforming elements 132 and 134 which shape tissue into a semi-circularcross-sectional shape, between a forming surface 136 on the firstforming element 132 and a forming surface 138 on the second formingelement 134. Again, it should be understood that other shapes areconceivable and consequently are included within the scope of theinvention.

[0058] In addition to three-dimensional shaped parts, it is alsopossible to make a flat piece of graft material. Forming elements likethose shown in FIG. 4E are useful in this case. For example, a skingraft may be placed on an adhesive based mesh (possibly using fibrin) onthe flat forming surface 128. The cells are then subjected to pressureto adhere them together. The cells are spread out over a finer layer. Aflat, even, piece of skin graft material is formed. This can then be cutor pressed or formed into a specific shape and then used as a skinsubstitute on the body.

[0059] Any forming element useful in the present invention can be coatedwith a non-stick coating to reduce adhesion of the compressed tissue tothe forming elements. For example, the forming element 100 (FIG. 4B) isindicated as having a non-stick coating 105 such as a Teflon™. coatingwhich may be applied in any suitable known manner. Such a coating canresist the binding of the tissue (or tissue additive such as fibrindiscussed below) to the forming element 100. In a second embodiment ofthe invention, illustrated in FIG. 5, a tissue press 150 is fluidoperated (pneumatic or hydraulic) rather than manually operated. Thepress 150 includes a base 152 having a support surface 154 forsupporting the base 152 and thus the press 150 on a table 15 or othersupport (not shown). A first forming element 156 is attached to the base152. The first forming element 156 may be slidably or otherwise attachedto the base 152 in any suitable manner which blocks movement of theforming element 156 relative to the base 152 during operation of 20 thepress 150 and which allows for easy interchange of forming elements 156.The first forming element 156 has an upwardly facing forming surface158. A fluid drain opening 160 is in fluid communication with theforming surface 158 of the first forming element 156.

[0060] An air or hydraulic cylinder 170 is fixed to the base 152 abovethe first forming element 156. The cylinder 170 has a port 172 for theintroduction of air or other fluid under pressure to operate a piston174 in a known manner. A second forming element 180 is connected to thepiston 174. The second forming element 180 is attached to the piston 174in any suitable manner which blocks movement of the forming element 180relative to the piston 174 during operation of the press 150 and whichallows for easy interchange of forming elements 180. The second formingelement 180 has a forming surface 182 facing the forming surface 158 onthe first forming element 156.

[0061] A port 176 in the cylinder 170 is in fluid communication with theforming surface 182 of the second forming element 180. Connected to theport 176 is a pressure monitor device shown schematically at 178.

[0062] In operation of the press 150, a pair of forming elements 156 and180 are selected which when brought together will shape tissue to thedesired shape. The first forming element 156 is attached to the base152. The second forming element 180 is attached to the piston 174. Apiece of tissue to be shaped (not shown) is placed between the first andsecond forming elements 156 and 180. The piece of tissue is preferablypositioned on the forming surface 158 of the first forming element 156.

[0063] The cylinder 170 is then actuated to move the second formingelement 180 toward the first forming element 156. The forming surface182 on the second forming element 180 engages the tissue, and forces thetissue against the forming surface 158 on the first forming element 156.Pressure on the tissue is controlled through observation of the monitordevice 178. The tissue is formed to the desired shape. Again, it shouldbe understood that with the press 150 tissue can be reshaped only, orcompressed also, depending on the application, the forming elementsselected, and the amount of force applied.

[0064] As discussed above, when tissue is compressed, fluid may beexpressed from the tissue. In the press 150, the second forming element180 fits within the first forming element 156 to define between them aclosed forming chamber in which the tissue is compressed. Expressedfluid is drained from the forming chamber through the fluid drainopening 160. If a closed forming chamber is not formed, as for examplewith the open-ended forming elements shown in FIG. 1-4, then expressedfluid can drain outwardly from the tissue being pressed, without theneed for a separate fluid drain port. Of course, a separate fluid drainport could be provided in any of the forming elements of the presentinvention.

[0065] In a third embodiment of the invention, illustrated in FIG. 6, atissue press 200 includes a base 202 having a support surface 204 forsupporting the base 202 and thus the press 200 on a table or othersupport (not shown). A first forming element 206 is attached to the base202. The first forming element 206 may be slidably or otherwise attachedto the base 202 in any suitable manner. The first forming element 206includes a plurality of first fingers 208 which together have a formingsurface 210 to progressively compress bone or other tissue into apredetermined shape.

[0066] An upper arm 220 is pivotally mounted to the base 202 by a pivotpin 222. A second forming element 224 is connected to the upper arm 220in a suitable manner. The second forming element 224 includes aplurality of second fingers 226 which together have a forming surface228 facing the forming surface 210 on the first forming element 206. Thesecond fingers 226 are interdigitable with the first fingers 208.

[0067] In operation of the press 200, a pair of forming elements 206 and224 are selected which when brought together will progressively shapetissue to the desired shape. The first forming element 206 is attachedto the base 202. The second forming element 224 is attached to the upperarm 220. A piece of tissue to be shaped (not shown) is placed betweenthe first and second forming elements 206 and 224. The piece of tissueis preferably positioned on the forming surface 210 of the first formingelement 206. The upper arm is pivoted toward the base to move the secondforming element 224 toward the first forming element 206. The formingsurface 228 on the second forming element 224 engages the tissue, andforces the tissue against the forming surface 210 on the first formingelement 206. The tissue is formed to the desired shape.

[0068] Because the second fingers 226 are interdigitable with the firstfingers 208, the press 200 is operable to compress tissue to differentcompressed sizes with only one pair of forming elements. As the secondfingers 226 come together with the first fingers 208, they compress thetissue to a smaller and smaller diameter (shape). This allows for onepair of forming elements to provide compression to variable diameters orsizes. This works well with soft tissue applications, specificallytendons, to compress the tendon into a smaller shape. The amount ofcompression is based on the amount of pressure applied and the neededfinished size.

[0069] As noted above, it is important to control the pressure or forceapplied to the tissue by the tissue press. Accordingly, the presentinvention provides means for limiting the amount of pressure applied tothe tissue by the tissue press, that is, means for blocking applicationto the tissue of force in excess of a predetermined amount. Such meansare schematically illustrated in FIG. 6A, which illustrates a tissuepress 300 having a known torque wrench assembly included therein.

[0070] The press 300 includes a base 302. Attached to the base in themanner described above is a first forming part 304. Also attached to thebase is a saddle 306. Received in the saddle 306 is the connectorportion 308 of a handle assembly 310. The press 300 also includes apivot pin 312 pivotally interconnecting the handle assembly 310 and thebase 302.

[0071] The handle assembly 310 includes a form-supporting portion 314 towhich there is attached in the manner described above a second formingpart 316. The handle assembly 310 also includes a second portion 318connected to the form-supporting portion 314 by a drive mechanism 320.The second portion 318 includes a knurled section 322 which is rotatableabout an axis 324. On the second portion 318 there is a gauge 326.

[0072] The knurled section 322 is rotatable about the axis 324 to setthe torque value desired and as shown on the gauge 326. Thereafter, thehandle assembly 310 can be pivoted toward the base 302 in the directionindicated by the arrow 328 only until the preset amount of torque isapplied. At that point, no more torque is transferred through the drivemechanism 320 to the form-supporting portion 314. This limits the amountof pressure applied to the tissue by the second forming part 316, thatis, blocks application to the tissue of force in excess of apredetermined amount.

[0073] It should be understood that the torque wrench assembly orconstruction indicated in FIG. 6A is only illustrative of the many waysin which the amount of pressure applied to the tissue by the tissuepress can be limited to a predetermined amount. There are other knownmechanisms for performing the same function, and their use is includedwithin the scope of the present invention.

[0074]FIGS. 7 and 7A illustrate the use of a tissue press in accordancewith the present invention to form a composite graft. As discussedabove, with the present invention, it is also possible to make acomposite graft. For example, the graft material for an anteriorcruciate ligament reconstruction is preferably tendon in the middle withbone at both ends. In accordance with the apparatus and method of thepresent invention, bone tissue can be compressed around the ends oftendon tissue to form a substitute anterior cruciate ligament moreclosely approximating the original.

[0075] Thus, as illustrated schematically in FIGS. 7 and 7A, the tissuepress 10 of FIG. 1-4 is being used to compress bone tissue 240 aroundtendon tissue 242 to form a substitute anterior cruciate ligament 244.The tendon 242 can be harvested from one site and the bone 240 can beharvested from another site.

[0076] It should be understood that the graft can be multiple tissuefragments rather than a composite material. Thus, the tissue press 10,or indeed any tissue press in accordance with the present invention, canbe used to compress, for example, multiple bone fragments into onelarger piece. It should also be understood that the tissue press inaccordance with the present invention can be used to add additionalmaterials to body tissue material by pressure. For example, to bonetissue there can be added tri-calcium phosphate, an antibiotic,hydroxyapatite, allografts or autografts, or any other polymeric. Thisprocess is believed to be self-explanatory in light of the foregoingdescription, but for reference may be understood by referring to FIGS. 7and 7A wherein 240 would be the bone tissue or other tissue to whichmaterial is being added (squeezed in under pressure), and 242 indicatesthe additional material being added to the tissue 240.

[0077] In this case, fibrin can be highly suitable for use as such anadditional material. Fibrin is a blood component important in bloodclotting. It can be separated or centrifuged from blood and has thenature of an adhesive gel. Fibrin can be used as an adhesive, either ina natural state or after being compressed, to hold together materialsuch as separate tissue pieces pressed together in a tissue press of thepresent invention.

[0078] In a fourth embodiment of the invention, illustrated in FIG. 8, atissue press 250 is operated to extrude rather than press material. Thepress 250 includes a base 252 having a support surface 254 forsupporting the base 252 and thus the press 250 on a table or othersupport (not shown). A die 256 is attached to the base 252. The die 256may be slidably or otherwise attached to the base 252 in any suitablemanner which blocks movement of the die 256 relative to the base 252during operation of the press 250 and which allows for easy interchangeof forming elements 256. The die 256 has an upwardly facing opening 258.An extrusion opening 260 is in fluid communication with the opening 258of the die 256.

[0079] An air or hydraulic cylinder 270 is fixed to the base 252 abovethe die 156. The cylinder 270 has a port 272 for the introduction of airor other fluid under pressure to operate a piston 274 in a known manner.A ram 280 is connected to the piston 274. The ram 280 has a surface 282facing the opening 258 on the die 256.

[0080] In operation of the press 250, a die 256 is selected which willextrude tissue in the desired shape. The die 256 is attached to the base252. A piece of tissue to be extruded (not shown) is placed in theopening 258 of the die 256. The cylinder 270 is then actuated to movethe ram 280 toward the die 256. The surface 282 on the ram 280 engagesthe tissue, and forces the tissue into and through the die 256, exitingthrough the opening 260. The tissue is extruded in the desired shape. Asdiscussed above, a fluid drain port can be provided in the press 250.

[0081] It can also be useful to heat or cool the tissue being worked ina tissue press of the present invention. Accordingly, the presentinvention contemplates the use of means for selectively controlling thetemperature of the piece of tissue while it is being compressed orshaped. As an example, illustrated schematically in FIG. 4 is a fluidpassage 284 extending from the outer surface of the forming element 124and around the forming surface 128 thereof. Fluid which is either heatedor cooled flows through the passage 284 and either cools or heats thematerial of the forming element 124 in the area adjacent the formingsurface 128. Thus, the tissue, when it comes in contact with the formingsurface 128, can be selectively heated or cooled during the compressionor reshaping operation. Heating can be useful in holding togethermaterials being compressed, for example, and cooling can be useful toavoid tissue damage arising from overheating of tissue being compressed.It should be understood that other means of achieving these functionsare contemplated, such as electrical heating elements. Further, bothforming elements can be heated or cooled rather than just one. Any suchequivalent structure is to be considered within the scope of the presentinvention.

[0082] Also in the present invention, a retainer is provided forretaining tissue graft material in its compressed state. After the graftis compressed, the retainer is placed around the graft. The retainer canhelp to maintain the graft in a compressed configuration or in aspecific shape for a period of time long enough to be placed in thebody.

[0083] The retainer may be one of many different shapes. The shape ofthe retainer is chosen to meet the specific application. There are anumber of suitable shapes, such as a ring, a cylinder, a cage, arectangular shape, a mesh, a suture-like wrap, etc. Some of these areillustrated schematically in FIG. 9A-9F. It should be understood thatthis is not an exhaustive listing, but rather that these are merelyexemplary of the principle involved, and accordingly, the invention isnot limited to these particular shapes. For example, a retainer may beprovided which is in the particular shape of the tissue material beingcompressed, which can be rectangular, cylindrical, planar, etc.

[0084]FIG. 9A illustrates a plurality of bands or rings 290 used to holdtogether compressed tissue 292. FIG. 9B illustrates a cage 294 which canbe used to hold together the compressed tissue 292 of FIG. 9A. The cage294 includes a plurality of crossed filaments 296 which define betweenthem a series of openings 298 for tissue ingrowth. FIG. 9C illustratesanother cage 300 which can be used to hold together the compressedtissue 292 of FIG. 9A. The cage 300 includes a plurality oflongitudinally extending filaments 302 which define between them aseries of openings 304 for tissue ingrowth. FIG. 9D illustrates asolid-walled cylinder 306 which can be used to hold together thecompressed tissue 292. FIG. 9E illustrates a mesh cylinder 308 which canbe used to hold together the compressed tissue 292. FIG. 9F illustratesthe wrapping of a cord or suture 310 around compressed tissue 312.

[0085] Any of these retainers may be made of various materials. Thematerial of the retainer is chosen to meet the specific application.Some of the many materials which are suitable are biodegradablematerials, ceramics (especially with bone-growth enhancers,hydroxyapatite, etc.); polymeric material such as Dacron® or other knownsurgical plastics; metal; or composite materials.

[0086] In use, the graft material may be pushed into the retainerstructure after graft material is compressed. Alternatively, the graftmaterial may be compressed with the retainer structure. After the graftmaterial is compressed in the retainer, the combined structure of graftplus retainer is placed in the host site in the body. The retainer helpsto maintain the graft in a compressed configuration or in the specificshape into which it was compressed for a period of time long enough tobe placed in the body.

[0087] If the retainer is made of a biodegradable material, then theretainer degrades and disappears after a period of time. If the retaineris not made of a biodegradable material, then the retainer remains inthe body. Tissue ingrowth occurs to bind the host tissue to the graftmaterial. Tissue ingrowth through and around the retainer, between thehost tissue and the graft material, is promoted if there are openings asdiscussed above in the retainer.

[0088] The invention, the retainer may, if desired, be made of amaterial which expands after it is placed in the body, to mechanicallyinterlock the graft to the body. The expansion can take place in one oftwo ways. First, the retainer can itself be compressed, as with thetissue, and then expand when placed in the body. Second, the retainercan be made of a material which expands when it comes in contact withwater or other bodily fluids. (It should be noted that the tissue canitself be compressed then expand when contacted by water. As an example,a tendon can be compressed in a desiccated state, and as it imbibeswater it expands and creates a firmer lock or tighter fit in the hostsite.)

[0089] The expandable material can first be compressed with the tissuebeing grafted, and which then expands when placed in the body. Theretainer is preferably made of a material which has more structuralstability than the tissue being grafted, and provides mechanicalintegrity and structural support for the graft tissue. A retainer madeof a solid polymeric material, for example, is useful to retain in acompressed state a tendon or bone tissue graft.

[0090] These expandable materials can be used not only to retain graftmaterial, but for any shape required for stabilization surgery, such asa wedge, screw, rivet, retaining ring, or spacer, an intramedullary rod,a joint replacement part such as a femoral component of acetabular cup,an expandable sleeve, or another mechanical structure. The expandablematerials thus can be used both as a carrier or retainer for anothermaterial (e.g. tissue graft material) and on their own as a prostheticelement.

[0091] There are a number of suitable materials which expand when theycome in contact with water or other fluids. One is PEEK(polyether-etherketone). A desiccated biodegradable material, or adesiccated allograft may also be used.

[0092] As a simple example, an expandable retainer 330 (FIG. 10B) withgraft tissue 332 therein is placed into a tissue or bone space 334defined by an edge 336 in host tissue 38. As the retainer 330 imbibesbody fluids or water from the host tissue 338, it expands radiallyoutwardly into the tissue or bone space 334 and creates a mechanicalinterlock (FIG. 10A). It also expands radially inwardly and clamps onthe graft tissue 332. Therefore, the graft tissue 332 is locked into thehost site, without the necessity of damaging the tissue further throughsome other kind of attachment means.

[0093] For example, a hip replacement (femoral head) is typically madeof metal. To implant the replacement, the softer, inner cancellous boneof the femur is first removed. The inner surface of the cortical bone isthen machined to provide a close fit between the external surface of thereplacement and the hard outer cortical bone material. All this requiresa substantial opening in the femur and still does not guarantee a closeenough fit for the implant.

[0094] If, instead, the implant is made of an expanding material such asPEEK, only a smaller opening is needed, thus reducing trauma to thebone. Although it is best to lock against the cortical bone, it ispossible to implant solely in the cancellous bone, which because of theexpansion of the implant provides a better fit than a metal implant. Abenefit of implanting in the cancellous bone is reduction of the dangerof putting the implant in so tightly that the cortical bone is split(wedged open). Further, if the opening in the bone is not exactly thesame shape as the outer surface of the implant, the implant expands toprovide a custom contoured fit to the bone and provide immediatemechanical stability. Thus, less machining of the bone is needed, whileat the same time obtaining a closer fit.

[0095] Thus, as illustrated in FIG. 11-11B, a hip replacement (femoralhead) 340 is made of PEEK or another expandable material. Thereplacement 340 is inserted into an intramedullary channel 342 cut intoa femur 344. The replacement 340 is smaller in diameter than the channel342. The replacement 340 absorbs body fluids and expands to lock itselfinto the channel 342 in the femur 344. (It should be understood that thescale shown in FIG. 11-11B is exaggerated as to the amount by which thereplacement 340 expands.)

[0096] Similarly, a bone plate or other structure or tissue can besecured to a bone with a fastener made of such an expandable material.As illustrated schematically in FIGS. 12 and 12A, a bone plate 350 issecured to a bone 352. In FIG. 12, a fastener 354 is used which has anunthreaded portion 356 extending into the bone 352. The fastener 354, orat least the unthreaded portion 356, is made of PEEK or another suitableexpandable material. The portion 356 imbibes fluid from the bone 352 andexpands radially outwardly, from an unexpanded condition as shown inphantom at 358 to an expanded condition as shown in solid lines at 360,to lock the fastener 354 into the bone 352. This enables the securing ofthe plate 350 to the bone 352 without cutting threads into the bone 352as is usually done.

[0097] In FIG. 12A, a fastener 362 has a threaded portion 364 extendinginto the bone 352. The threaded portion 364 is made of PEEK or anothersuitable expandable material. The threaded portion 364 imbibes fluidfrom the bone 352 and expands radially outwardly to additionally lockthe fastener 362 into the bone 352. Alternatively, the fastener 362 ofFIG. 12A may have a coating 366 on its portion threaded into the bone352. The coating 366 is made of PEEK or another suitable expandablematerial. The coating 366 imbibes fluid from the bone 352 and expandsradially outwardly to additionally lock the fastener into the bone 352.

[0098] When such a fastener is made of a non-metal expandable material,removal of the fastener simply entails drilling out the center thereof.This is much easier than with a typical metal bone screw.

[0099] From the above description of the invention, those skilled in theart will perceive improvements, changes and modifications. Suchimprovements, changes and modifications within the skill of the art areintended to be covered by the appended claims.

That which is claimed is:
 1. An implant used for stabilizing body tissuecomprising: a core at least partially formed of a material which expandsby imbibing fluid, and a retainer at least partially enclosing the core.2. An implant as defined in claim 1 wherein the core is at leastpartially formed of a desiccated material.
 3. An implant as defined inclaim 2 wherein the retainer includes a plurality of crossed filaments.4. An implant as defined in claim 3 wherein the retainer includes aplurality of openings.
 5. An implant as defined in claim 4 wherein theretainer is at least partially made of a polymeric material.
 6. Animplant as defined in claim 1 wherein the core is at least partiallyformed of desiccated allograft material.
 7. An implant as defined inclaim 6 wherein the retainer is a cage.
 8. An implant as defined inclaim 7 wherein the retainer includes a plurality of openings.
 9. Animplant as defined in claim 8 wherein the retainer is at least partiallymade of ceramic.
 10. An implant as defined in claim 9 wherein theretainer includes bone growth enhancers.
 11. An implant as defined inclaim 10 wherein the retainer includes hydroxyapatite.
 12. An implant asdefined in claim 1 wherein the core is at least partially formed of abiodegradable material.
 13. An implant as defined in claim 12 whereinthe biodegradable material is desiccated.
 14. An implant as defined inclaim 13 wherein the retainer is a mesh.
 15. An implant as defined inclaim 14 wherein the retainer includes a plurality of openings.
 16. Animplant as defined in claim 15 wherein the retainer is at leastpartially made of composite material.
 17. An implant used forstabilizing body tissue comprising: a core at least partially formed ofa material which expands after being compressed, and a retainer at leastpartially enclosing the core.
 18. An implant as defined in claim 17wherein the core is at least partially formed of a biodegradablematerial.
 19. An implant as defined in claim 18 wherein the retainerincludes a plurality of longitudinal filaments.
 20. An implant asdefined in claim 19 wherein the retainer includes a plurality ofopenings.
 21. An implant as defined in claim 20 wherein the retainer isat least partially formed of metal.
 22. An implant as defined in claim17 wherein the core is at least partially formed of a material whichexpands by imbibing fluid.
 23. An implant as defined in claim 22 whereinthe material which expands by imbibing fluid is desiccated.